Degradation of a turbocharger may be reduced by limiting turbocharger operation to selected operating conditions. In U.S. Patent Application 2009/0090107 a model is used to estimate turbocharger speed, and a turbine actuator control law is estimated by mapping the turbine from a measurement of flow into the turbine and from a desired ratio of the pressures in the turbine. The approach then adjusts a turbine actuator to modify the turbocharger turbine geometry. The actuator modifies the flow rate to the turbine so that pressure in the intake manifold is equal to a set point pressure. However, the method appears to overlook that it may be undesirable to operate the turbocharger at a turbine expansion ratio that exceeds a turbine expansion ratio limit. Consequently, the approach may accelerate turbocharger degradation during some operating conditions.
The inventors herein have recognized engine operating conditions where it may not be desirable to operate an engine when a turbine expansion ratio exceeds a turbine expansion ratio limit. Further, the inventors have recognized that different turbine expansion ratio limits are desirable for different exhaust gas flow rates. For example, it may not be desirable to operate an engine to regenerate a particulate filter when regenerating the particulate filter or the method of regenerating the particulate filter can cause a turbine expansion ratio to exceed a turbine expansion ratio limit. Further, if an operator fails to change an air cleaner element, the turbine expansion ratio limit may be exceeded thereby leading to turbocharger degradation. However, it may be desirable to permit a higher turbine expansion ratio limit at low engine speeds when exhaust gas flow rates are lower and turbocharger degradation is less likely so that the driver may have an expected level of engine performance or particulate filter regeneration function.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: operating an engine with a turbocharger; adjusting operation of the engine in response to a turbine expansion ratio exceeding a turbine expansion ratio limit of the turbocharger, the turbine expansion ratio limit varying in response to an exhaust gas flow rate.
By adjusting operation of an engine in response to a turbine expansion ratio limit, engine operation can be limited such that the possibility of turbocharger degradation may be limited. For example, if a particulate filter is scheduled to regenerate a higher altitude the particulate filter regeneration can be delayed until then engine is at a lower altitude or different operating mode when regeneration can be enabled. Further, if during normal engine operation the turbine expansion ratio exceeds a desired expansion ratio limit, the engine output or other operating parameters can be reduced so as to reduce the possibility of operating the turbocharger turbine at an expansion ratio that exceeds a turbine expansion ratio limit.
The present description may provide several advantages. For example, the approach may reduce the possibility of turbocharger degradation. Further, the approach may provide an improved basis for turbine expansion ratio limits. Further still, the approach may be beneficial for improving a variety of engine operating conditions including particulate filter regeneration and engine operation with reduced intake system capacity.
Furthermore, the inventors herein have recognized that although a reduction in engine output during steady state conditions may reduce the possibility of operating the turbocharger turbine at an expansion ratio that exceeds a turbine expansion ratio limit, a reduction by the same amount during transient conditions may cause the turbocharger turbine to operate at an expansion ratio that exceeds the limit. In some cases, such expansion ratio limit violations during transient conditions may be due to a response time of the turbocharger not reacting fast enough to compensate for the expansion ratio change. For example, during transient accelerations exhaust flow and temperature may increase at a faster rate than a turbine actuator can react to compensate for the increase.
Further, in some cases, such expansion ratio limit violations during transient conditions may be due to the expansion ratio changing slower than during steady state conditions. For example, during transient decelerations (e.g., tip out of the accelerator pedal), the mass moment of inertia may cause engine speed to be increased for a short period even after toque has dropped that causes air to be continued to be pumped into the engine. The continued pumping of air may cause an increase in the turbine expansion ratio that violates the turbine expansion ratio limit. Continuous violations of these limits during transient conditions may cause degradation of the turbine actuator.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: operating an engine with a turbocharger; during a steady state condition, adjusting operation of the engine in response to a turbine expansion ratio exceeding a first turbine expansion ratio limit of the turbocharger; and during a transient condition, adjusting operation of the engine in response to a turbine expansion ratio exceeding a second turbine expansion ratio limit of the turbocharger that differs from the first expansion ratio limit. For example, the first and second turbine expansion ratio limits may vary in response to an exhaust gas flow rate. For a given exhaust gas flow rate, the first and second expansion ratio limits may differ. In one particular example, the second limit may be less than the first limit.
By separately calibrating the expansion ratio limits for steady state conditions and transient conditions, the expansion ratio limit may be made more restrictive during transient conditions in order to compensate for increased expansion ratio changes. Correspondingly, the expansion ratio limits may be made less restrictive during steady state conditions in order to reduce the possibility of needlessly reducing engine output or other operating parameters. In this way, a possibility of operating the turbocharger turbine at an expansion ratio that exceeds a turbine expansion ratio limit may be reduced even as operating conditions of the engine vary between steady state conditions and transient conditions while reducing the possibility of needlessly reducing engine output.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.